A plastic ruler is much easier to bend in one direction than another according to the proportionality shown, where b is the breadth and d is the depth of the rectangular cross-section.

The ruler can be approximated as being 1mm thick and 20mm wide.

How much stiffer is it in the hard-to-bend direction?

The problem was suggested by Leslie Green.

WARNING: Unless the ruler has some sort of anti-shatter statement written on it, do not try bending it like this without using eye protection. Older designs of rulers are known to shatter and eject bits of plastic into nearby eyes.